PART TIME TYPE FOUR-WHEEL-DRIVE VEHICLE

PURPOSE:To prevent a differential gear from being subjected to excessive loads by forcing a vehicle into a four wheel drive condition when a transmission is shifted to an ultra-low speed position. CONSTITUTION:When a drive change-over switch 11 is connected with an ultra- low speed change-over switch 10, an atmosphere releasing valve 6 makes No.1 chamber 2b atmospheric in pressure and simultaneously a negative pressure transmitting valve 5 makes No.2 chamber 2c negative in pressure while No.2 chamber is communicated with a reservoir tank 7. With this, a diaphragm 2a moves upward allowing a lever 1 to be titled to the direction A so as to allow a vehicle to perform a four wheel drive. Under this condition, a change- over to an ultra-low speed running condition causes the switch 10 to be changed allowing the closing condition of the valves 5 and 6 to be changed reversely. Accordingly, No.1 chamber 5b will be negative in pressure and No.2 chamber 5c will be simultaneously atmospheric in pressure causing the diaphragm 2a to be displaced so as to allow the vehicle to be in the four wheel drive condition.